1. Field of the Invention
The present invention generally relates to an air intake system for a vehicle combustion engine and, more particularly, to the air intake system for supplying a combustion air to the engine mounted on a motorcycle.
2. Description of the Prior Art
The air intake system hitherto employed in a motorcycle will be discussed with particular reference to FIGS. 8A to 8C. As shown in FIG. 8A, the motorcycle has a fairing or front cowling 51 having an air intake opening or air scoop 50 defined therein so as to open forwardly at a location substantially below a headlight 52 for introducing a combustion air A for use in a motorcycle internal combustion engine (not shown). The air scoop 50 is in communication with an air intake duct 55 which is in turn in communication with the motorcycle internal combustion engine in any known manner well known to those skilled in the art.
According to the conventional air intake system shown in FIG. 8A, where the combustion air entering the air scoop 50 is directed to flow over the internal combustion engine towards the rear of the engine, a portion of the air intake duct 55 has to be bent upward so as to extend above the engine. Bending of the air intake duct 55 tends to result in occurrence of a turbulent flow of air being introduced, accompanied by an increased flow resistance enough to reduce the ram pressure of the combustion air being introduced through the intake duct 55.
In the illustrated conventional air intake system, since the point of stagnation SP of the air A flowing along the fairing or front cowling 51 is located around the upper end of the air scoop 50 as shown in FIG. 8A, the conventional air intake system have additional problems. Specifically, when the front or “head” of the motorcycle lowers down due to suspension settings, the stagnation point SP shifts relatively upwardly from the air scoop 50 as shown in FIG. 8B to such an extent as to result in reduction in ram pressure.
On the other hand, when the motorcycle then traveling forwards is, for example, accelerated rapidly with the head of the motorcycle consequently raised upwardly as shown in FIG. 8C, there arises an area S in which a current of air A flowing from below is incapable of entering into the air intake duct 55 through the air scoop 50, being blocked by a lower peripheral lip region 53 of the air scoop 50. Once this occurs, an air intake stream is substantially narrowed and thus, the air A ready to enter the air intake duct 55 will not be sufficiently introduced through the air scoop 50, resulting in reduction of the ram pressure.
If an attempt is made to tailor a lower inner surface 53a adjacent the lower peripheral lip region 53 of the air scoop 50 to represent a downwardly curved guide face to facilitate entry of the air A into the air intake duct 55 through the air scoop 50, because of the presence of a front fender or mudguard above a front wheel, a difficulty is encountered in securing a sufficient space for defining the guide face.
As discussed above, with the conventional air intake system, the ram pressure of the air being introduced tends to vary depending on the position or “posture” of the motorcycle during its travel.
On the other hand, the air intake system is also known in which the air scoop is defined at a relatively high level so as to assume a position between left and right headlights. See, for example, the Japanese Laid-open Patent Publication No. 2001-71968 and, particularly, the paragraph [009] and FIG. 3 thereof. According to this prior art air intake system, the problems discussed hereinabove with reference to FIGS. 8A to 8C may be resolved satisfactorily, but the number of component parts tends to increase with a consequent increase of the cost of manufacture since the left and right headlights have to be disposed independently from each other.